Summary: Multiple sclerosis (MS) is a T cell mediated autoimmune disease that is strongly associated with the expression of particular alleles of the class II HLA complex; however, the mechanism(s) by which the class II molecules confer susceptibility remains to be discovered. A favored hypothesis has been one in which HLA alleles help shape the responding autoreactive T cell repertoire via selective binding of disease-inducing self determinants, which favor the activation and expansion of pathogenic autoreactive T cells. However, the discernment of the influence exerted by expression of specific class II alleles is confounded by the observed disparity in concordance rates and disease severity among individuals of the same HLA haplotype. At issue is whether such highly-related individuals recruit and expand identical T cell clonotypes, as determined by sequences in the TCR hypervariable regions, in response to challenge with a define antigenic challenge. Recently, we reported that NOD (H- 2g7) and NOD.B10.Idd9 (H-2g7) mice are highly susceptible to the induction of EAE with the encephalitogenic peptide MOG35-55 (myelin oligodendrocyte glycoprotein), while only a small percentage of NOR/LtJ (H-2g7) mice develop clinical disease - an acute self-limiting EAE. Our preliminary data indicated that BV8.2BJ2.7-expressing MOG-specific Th cells were present in the lymphoid tissue and CNS of NOD mice with EAE, but were undetectable in NOR/LtJ mice, despite their expression of a potent cellular immune response dominated by V beta 8+ Th cells. Since CDR1 and CDR2 of the TCR V beta 8 chain are encoded by BV8, our findings suggests that the MOG reactive T cell repertoires in NOD and NOR/LtJ mice differ significantly in sequences found in the CDR3 of the TCR beta chain. To determine if T cell clonotypes with a unique CDR3 can be associated with progressive EAE, we will determine if NOD (H-2g7) and NOD.B10.Idd9 (H-2g7) mice, call upon a distinct public Th repertoire, BV8.2BJ2.7-expressing, I-Ag7-restricted T cells, following immunization with MOG35-55. Secondly, we will determine if the putative public clonotype is recruited and expanded in MHC-matched NOR/LtJ (H-2g7) mice. Furthermore, since the antigenic determinant contains amino acids that interact with critical residues in the pocket of the I-Ag7 molecule, and others that interact directly with the complementarity determining regions (CDR) of the TCR variable regions, we will resolve the fine antigenic specificity of the dominant MOG clonotypes in each strain, with an emphasis on those that enter the CNS. Our goal is to determine if the molecular interactions between sequences encoded by BV, BD, and BJ, which shape CDR3, and residues of the antigenic peptide are influential in differentiating benign autoimmunity from pathogenic inflammatory autoimmune disease. The goal of this proposal is to understand the role of T cell repertoire selection and TCR hypervariable region structure (CRD3) in the pathogenesis of the T cell mediated autoimmune disease EAE, a murine model of multiple sclerosis. The investigation will use three highly related mouse strains to determine if the expression of unique T cell clonotypes can distinguish benign autoimmunity from pathogenic inflammatory autoimmune disease in the CNS. [unreadable] [unreadable] [unreadable]